Vibration damping system for drilling equipment

ABSTRACT

A downhole tool is described designed to be suspended from a surface location into a wellbore ( 11 ), the tool including at least one module ( 20 ) with elements susceptible to mechanical vibrations or shocks, having the module coupled to remaining parts of the tool with one or more transducers ( 31 ) comprising electroactive polymeric material.

The present invention generally relates to an apparatus and a method forvibration damping to damp vibrations produced when drilling a well. Morespecifically, it pertains to such an apparatus and method for protectingsensitive components, particularly electronic components, from shocksand vibrations generated while drilling.

BACKGROUND OF THE INVENTION

Various well logging and monitoring techniques are known in the field ofhydrocarbon and water exploration and production and CO2 sequestration.These techniques employ downhole tools or instruments equipped forexample with sources adapted to emit energy through a boreholetraversing the subsurface formation. The emitted energy passes throughthe borehole fluid (“mud”) and into the surrounding formations toproduce signals that are detected and measured by one or more sensors,which typically are also disposed on the downhole tools. By processingthe detected signal data, a profile of the formation properties isobtained.

A downhole tool, comprising a number of emitting sources and sensors formeasuring various parameters, may be lowered into a borehole on the endof a cable, a wireline, a drill string or coiled tubing.

Based on the collection of data on downhole conditions during thedrilling process, the driller can modify or correct key steps of theoperation to optimize performance. Schemes for collecting data ofdownhole conditions and movement of the drilling assembly during thedrilling operation are known as Measurement While Drilling (MWD)techniques. Similar techniques focusing more on measurement of formationparameters than on movement of the drilling assembly are known asLogging While Drilling (LWD). Here, the operator can make or revisedecisions concerning the drilling and production of the well.

These tools are typically equipped with sensitive components, e.g.,electronics packages, boards and modules, that often are not designedfor such harsh environments. The trend among manufacturers of electroniccomponents is to address the high-volume commercial market, making itdifficult to find components for downhole tools that functioneffectively at high levels of vibrations and mechanical shocks.

The vibrations are typically caused by drilling activity. Drillinginvolves an axial load to the drill bit when the bit is in contact withthe formation at the bottom of the wellbore, while rotating the bit. Thevibrations have damaging effects on electronic instrumentation presentin the MWD and LWD tools.

Many efforts have been made to design mechanical devices to reduceoscillations, shocks, and vibrations. Some of the devices usereciprocating mandrels in combination with a compressible fluid filledchamber to absorb shocks and dampen vibrations, such as the devicedisclosed in U.S. Pat. No. 4,439,167 issued to Bishop et. al.

Other devices use a plurality of resilient elastomer elements orbelleville springs to absorb axial shocks, such as the floating subdisclosed in U.S. Pat. No. 4,844,181 issued to Bassinger.

Another class of devices uses floating pistons and compressible fluidfilled chambers to absorb axial vibrations, such as the device disclosedin U.S. Pat. No. 4,901,806 issued to Forrest. Another class of devicesuses a helically splined mandrel or annular springs to absorbvibrations, such as the drill string shock absorber disclosed in U.S.Pat. No. 3,947,008 issued to Mullins.

U.S. Pat. No. 3,265,091 issued to De Jarnett discloses another devicefor absorbing vibrations that includes a drill pipe having an innersteel tube and an outer steel tube. The annular space between the tubesis filled with a fluid of preselected density that acts to damp orabsorb vibrations. Similarly in the published European patentapplication EP-0414334 there is disclosed a shock absorber with a fluidchamber, in which a piston slides. The chamber has at least two openingsdiminishing hole area through which the fluid can escape from thechamber.

U.S. Pat. No. 6,364,039 B1 issued to Majkovic discloses a vibrationdamping apparatus including an annular housing, a cavity between aninternal diameter and an external diameter of the housing, and asubstantially solid vibration damping material disposed in the cavity.The vibration damping material has a density that is greater than thedensity of the housing material.

In view of the above art it is an object of the invention to provide asimple, robust and versatile apparatus and method for protectingsensitive components such as electronic boards or circuitry fromexposure to vibrations and shocks in a downhole environment,particularly while drilling.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the invention, there is provided adownhole tool designed to be suspended from a surface location into awellbore, said tool including at least one module with elementssusceptible to mechanical vibrations or shocks, wherein said module iscoupled to remaining parts of the tool with one or more transducerscomprising electroactive polymeric material.

In accordance with a second aspect of the invention, there is provided amethod for reducing the effects of accelerations on a module within adownhole tool, comprising the step of coupling said module to remainingparts of the tool with one or more transducers comprising electroactivepolymeric material; and lowering said tool into a subterranean wellbore.

In a preferred embodiment of the invention, the state of theelectroactive polymeric material is changed depending on the intensityand/or direction of the accelerations or vibrations, which arepreferably registered using suitable sensors, such as accelerometers.

In another preferred embodiment the use of the electroactive polymericmaterial is reversed to act as a harvesting tool to convert thevibrations into electric energy. This energy suitably accumulated andstored can be used for example to provide the power for the purpose ofdamping.

These and other aspects of the invention will be apparent from thefollowing detailed description of non-limitative examples and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of a LWD scenario, in which the presentinvention can be used;

FIG. 2 shows details of the LWD tool of FIG. 1 including an example ofthe invention; and

FIG. 3 is a schematic isolated view of an electronic boards protectedusing an example of the invention.

DETAILED DESCRIPTION

FIG. 1 illustrates a conventional drilling rig and drill string in whichthe present invention can be utilized to advantage. A land-basedplatform and derrick assembly 10 is positioned over a wellbore 11penetrating a subsurface formation F. In the illustrated embodiment, thewellbore 11 is formed by rotary drilling in a manner that is well known.Those of ordinary skill in the art given the benefit of this disclosurewill appreciate, however, that the present invention also findsapplication in directional drilling applications as well as rotarydrilling, and is not limited to land-based rigs, but can be equallyapplied to off-shore drilling.

A drill string 12 is suspended within the wellbore 11 and includes adrill bit 15 at its lower end.

The drill string 12 is rotated by a rotary table 16, energized by meansnot shown, which engages a kelly 17 at the upper end of the drillstring. The drill string 12 is suspended from a hook 18, attached to atraveling block (also not shown), through the kelly 17 and a rotaryswivel 19 which permits rotation of the drill string relative to thehook.

Drilling fluid or mud 26 is stored in a pit 27 formed at the well site.A pump 29 delivers the drilling fluid 26 to the interior of the drillstring 12 via a port in the swivel 19, inducing the drilling fluid toflow downwardly through the drill string 12 as indicated by adirectional arrow 9. The drilling fluid exits the drill string 12 viaports in the drill bit 15, and then circulates upwardly through theregion between the outside of the drillstring and the wall of thewellbore, called the annulus, as indicated by the direction arrows 32.In this manner, the drilling fluid lubricates drill bit 15 and carriesformation cuttings up to the surface as it is returned to pit 27 forrecirculation.

Drillstring 12 further includes a bottom hole assembly, generallyreferred to as 100, near the drill bit 15 (or in technical terms, withinseveral drill collar lengths from the drill bit). The bottom holeassembly includes capabilities for measuring, processing, and storinginformation, as well as communicating with the surface.

The bottom hole assembly 100 thus includes, among other things,measuring and local communications apparatus 200 for determining andcommunicating while drilling wellbore or formation parameters such asfor example the resistivity of the formation F surrounding the wellbore11. An example of apparatus 200, including transmitting antenna 205 andreceiving antenna 207, is described in detail in U.S. Pat. No.5,339,037, commonly assigned to the assignee of the present application,the entire contents of which are incorporated herein by reference.

The assembly 100 further includes a drill collar 130 for performingvarious other measurement functions, and surface/local communicationssubassembly 150. Subassembly 150 includes toroidal antenna 250 used forlocal communication with apparatus 200, and a known type of acousticcommunication system that communicates with a similar system (not shown)at the earth's surface via signals carried in the drilling fluid or mud.Thus, the surface communication system in subassembly 150 includes anacoustic transmitter which generates an acoustic signal in the drillingfluid that is representative of measured downhole parameters.

One suitable type of acoustic transmitter employs a device known as a“mud siren” which includes a slotted stator and a slotted rotor thatrotate and repeatedly interrupt the flow of drilling fluid to establisha desired acoustical wave signal in the drilling fluid. The drivingelectronics in subassembly 150 may include a suitable modulator, such asa phase shift keying (PSK) modulator, which conventionally producesdriving signals for application to the mud transmitter. These drivingsignals can be used to apply appropriate modulation to the mud siren.Again the electronic elements of the mud pulse telemetry system requiresprotection from the impact of vibrations and shocks and, hence, can beprotected using the present invention.

The generated acoustical wave is received at the surface by transducersrepresented by reference numeral 31. The transducers, for example,piezoelectric transducers, convert the received acoustical signals toelectronic signals. The output of transducers 31 is coupled to upholereceiving subsystem 90, which demodulates the transmitted signals. Theoutput of receiving subsystem 90 is then couple to processor 85 andrecorder 45.

Drill string 12 is further equipped in the embodiment of FIG. 1 withstabilizer collar 300.

Uphole transmitting system 95 is also provided, and is operative tocontrol interruption of the operation of pump 29 in a manner that isdetectable by transducers 99 in subassembly 150. In this manner, thereis two-way communication between subassembly 150 and the upholeequipment. Subassembly 150 is described in greater detail in U.S. Pat.No. 5,235,285, the entire contents of which are also incorporated hereinby reference. Those skilled in the art will appreciate that alternativeacoustic, as well as other techniques, can be employed for communicationwith the surface.

The power for all electrical systems including above mentioned elementsand the electronic components and sensors which from part of an exampleof invention as discussed below, is supplied as the turbine alternatoror positive displacement motor driven by the drilling mud, such as aMoineau-type motor (not shown). In other embodiments (not shown), powercould be supplied by any power supply apparatus including an energystorage device located downhole, such as a battery, or even supplied bywire or pressure pulses from the surface.

However, it should be noted that for the purpose of the presentinvention the exact purpose and components of the measuring andcommunication apparatus 200 or instrumentation of the bottom holeassembly 100 are not essential. Such apparatus can include anyconfiguration or module including transistors, integrated circuits,resistors, capacitors, and inductors, as well as electronic componentssuch as sensing elements, including antennae, accelerometers,magnetometers, photomultiplier tubes, sampling probes, pressure andstrain gages, timers, optical elements and the like. And in thefollowing an electric board is used to exemplify the above or othersimilar devices.

As shown in FIG. 2, an electronic module 20 for LWD applications istypically located inside a protective cylindrical housing 21, which ispreferably formed from stainless steel or a beryllium copper alloy. Thehousing 21 is either part of or enclosed within the drill string 12 asillustrated above. Depending on the specific embodiment a passage forthe flow of drilling mud is present either as shown in form of anannular passage 22 formed between the outer surface of the housing 21and the inner surface of the drill pipe 12 or (not shown) as a channelthrough the center of the drill string.

In the example the drilling mud flows through the annular passage 22 onits way to the drill bit 15, as previously discussed.

The electronic component 20 may, but according to the invention does notnecessarily, include one or more printed circuit boards associated withthe sensing device, as previously discussed. The module 20 can forexample be the control module, power regulator module, or pulsar module,or a sensor module etc. in which case the electronic component maydiffer in a way immaterial to the invention.

As shown in FIG. 2, the module 20 is at least partly mounted on adamping element 23 that includes an electroactive polymer (EAP) 231. Thepolymer is shown between two layers 232, 233 of an electricallyconducting material.

To illustrate the operating principle of the invention, a schematicdiagram of the above module is shown in FIG. 3 isolated from thesurrounding housing 21.

In FIG. 3 there is shown the module 20, mounted onto the top layer 232of conducting material. The space between the two layers 232, 233 isfilled with electroactive polymer material 231, possible composition ofwhich are described below. The three layers 231-233 form effectively acapacitor-type configuration, however, when applying a voltage betweenthe two layers 232, 233, the EAP layer 231 deforms or changes itsproperties, e.g. from a stiff to a elastic state. The configuration canhence also be regarded as being a transducer.

The deformation or state transition translates into either anacceleration of the mounted module 20 or a change in the stiffness withwhich the module 20 is coupled to the housing 21. Hence, by controllingthe voltage supplied to the layers 232, 233 and thus the deformation orstate of the EAP, the module can be accelerated into any direction asdefined by the design and location of the EAP material or,alternatively, coupled to its housing with a controllable stiffness.

The invention exploits the changeable properties of the EAP material byregistering shocks and vibrations using one or a plurality of shocksensors 31 which are part of the downhole tool. The sensors 31 can forexample be conventional accelerometers.

The shock sensors are used to drive directly or via a control loop apower source 32, which in turn alters the state of the EAP material atthe appropriate times to reduce the effect of any registeredacceleration, vibration or other mechanical shock. In the presentexample, the power source 32 is connected to the downhole generatorwhich supplies power to all components of the downhole tool.

It should be noted however that by reversing the above process,electrical power can actually be generated using the deformation of theEAP material to harvest electrical energy through the conversion of themechanical movement of the module 20 relative to the housing. Using forexample a charging circuit and a battery or a storage capacitor 33 theapparatus of FIGS. 2 and 3 can be used to generate and store electricpower.

By accumulating for example electric energy from low impact vibrationsand releasing the stored power to dampen potentially harmful vibrations,the system can be designed to operate quasi-autarkic.

A wide class of EAP materials are commercially available.

Generally, EAP can be divided into two major groups based on theiractivation mechanism including: ionic (involving mobility or diffusionof ions) and electronic (driven by electric field). A list of theleading EAP materials is given in Table 1 below.

TABLE 1 List of the EAP materials Electronic EAP Ionic EAP DielectricEAP Carbon Nanotubes (CNT) Electrostrictive Graft Conductive PolymersElastomers (CP) Electrostrictive Paper ElectroRheological Fluids (ERF)Electro-Viscoelastic Ionic Polymer Gels Elastomers (IPG) FerroelectricPolymers Ionic Polymer Metallic Composite (IPMC)

The electronic polymers (electrostrictive, electrostatic, piezoelectric,and ferroelectric) are driven by electric fields and can be made to holdthe induced displacement under activation of a dc voltage, allowing themto be considered for robotic applications. Also, these materials have agreater mechanical energy density and they can be operated in air withno major constraints. However, they require a high activation field(>100 MV/meter) close to the breakdown level.

In contrast, ionic EAP materials (gels, polymer-metal composites,conductive polymers, and carbon nanotubes.) are driven by diffusion ofions and they require an electrolyte for the actuation mechanism. Theirmajor advantage is the requirement for drive voltages as low as 1 to 2volts. However, there is a need to maintain their wetness, and exceptfor conductive polymers and carbon nanotubes it is difficult to sustaindc-induced displacements. The induced displacement of both theelectronic and ionic EAP can be geometrically designed to bend, stretch,or contract. Any of the existing EAP materials can be made to bend witha significant curving response, offering actuators with an easy to seereaction and an appealing response.

A particularly suitable EAP material is known for example from the U.S.Pat. No. 6,543,110 issued to Pelrine et al. and related patents andpatent applications as cited therein.

This particular material is known as pre-strained electroactivepolymers. When a voltage is applied to electrodes contacting apre-strained polymer, the polymer deflects. This deflection may be usedto do mechanical work. The pre-strain improves the mechanical responseof an electroactive polymer. The above referenced patent also describesthe details of manufacturing compliant electrodes that conform to theshape of a polymer and electromechanical devices.

Materials suitable for use as a pre-strained polymer with the presentinvention may include any substantially insulating polymer or rubberthat deforms in response to an electrostatic force or whose deformationresults in a change in electric field. One suitable material is NuSilCF19-2186 as provided by NuSil Technology of Carpenteria, Calif. Otherexemplary materials suitable for use as a pre-strained polymer include,any dielectric elastomeric polymer, silicone rubbers, fluoroelastomers,silicones such as Dow Corning HS3 as provided by Dow Corning ofWilmington, Del., fluorosilicones such as Dow Corning 730 as provided byDow Corning of Wilmington, Del., etc, and acrylic polymers such as anyacrylic in the 4900 VHB acrylic series as provided by 3M Corp. of St.Paul, Minn.

In many cases, materials used in accordance with the present inventionare commercially available polymers. The commercially available polymersmay include, for example, any commercially available silicone elastomer,polyurethane, PVDF copolymer and adhesive elastomer. Using commerciallyavailable materials provides cost-effective alternatives for transducersand associated devices of the present invention. The use of commerciallyavailable materials may simplify fabrication. In one embodiment, thecommercially available polymer is a commercially available acrylicelastomer comprising mixtures of aliphatic acrylate that are photocuredduring fabrication. The elasticity of the acrylic elastomer results froma combination of the branched aliphatic groups and crosslinking betweenthe acrylic polymer chains.

While the invention has been described in conjunction with the exemplaryembodiments described above, many equivalent modifications andvariations will be apparent to those skilled in the art when given thisdisclosure. Accordingly, the exemplary embodiments of the invention setforth above are considered to be illustrative and not limiting. Variouschanges to the described embodiments may be made without departing fromthe spirit and scope of the invention.

1. A downhole tool designed to be suspended from a surface location intoa wellbore, said tool including at least one module with elementssusceptible to mechanical vibrations or shocks, wherein said module iscoupled to remaining parts of the tool with one or more transducerscomprising electroactive polymeric material.
 2. The tool of claim 1,being a logging-while-drilling or measurement-while-drilling tool. 3.The tool of claim 1, wherein the module comprises an electronic board orcircuits.
 4. The tool of claim 1, wherein electroactive polymericmaterial changes its state depending on the intensity and/or directionof the vibrations or shock.
 5. The tool of claim 4, further comprising acontrol circuit to control a state of the electroactive polymericmaterial.
 6. The tool of claim 5, wherein the control circuit includesone or more vibration sensors.
 7. The tool of claim 5, wherein thecontrol circuit is programmed to apply a voltage or current to theelectroactive polymeric material.
 8. The tool of claim 1, including acircuit to convert deformation of the electroactive polymeric materialinto electrical energy and store said electric energy.
 9. The tool ofclaim 8, further comprising a control circuit to use the stored energyto drive the one or more transducers.
 10. A method for reducing theeffects of accelerations on a module within a downhole tool, comprisingthe step of coupling said module to remaining parts of the tool with oneor more transducers comprising electroactive polymeric material; andlowering said tool into a subterranean wellbore.
 11. The method of claim10, further comprising the step of changing the state of theelectroactive polymeric material depending on the intensity and/ordirection of the accelerations.
 12. The method of claim 11, furthercomprising the step of controlling the current or voltage applied to theelectroactive polymeric material in dependence of tool accelerations asmeasured by sensors.
 13. The method of claim 10, wherein deformation ofthe electroactive polymeric material is used to harvest energy from themechanical vibrations.
 14. The method of claim 13, wherein at least partof the energy required to activate the one or more transducers isobtained by the harvesting from mechanical vibrations.